"Infrared radiation" ("IR") refers to electromagnetic radiation having a wavelength longer than that of visible light. IR is associated with the radiation of heat. All bodies over absolute zero emit infrared radiation and the intensity increases monotonically with temperature.
Infrared images of radiant thermal energy can be used for diagnostic or comparative analysis. If the "normal" temperature characteristics of an object can be determined in relative or absolute terms, then abnormalities can be detected through infrared imaging. Among the uses for IR imaging devices are quality control inspections and preventive maintenance on industrial parts, remote sensing, surveillance and medical diagnosis.
Infrared video devices create a thermal image of an object by detecting and displaying relative intensities of infrared radiation emitted by the object, which then yields a measure of the temperature distribution. Because the imaging system responds only to changes in temperature, the infrared radiation reaching the detector from the object must be modulated to produce temperature differentials which may then be processed to determine absolute or relative temperature distribution.
One technique for modulating infrared radiation emitted by an object is to scan the object with a detector, either by moving the detector relative to a fixed object or by moving the object relative to a fixed detector. The detector then measures the differences between the temperatures of consecutive fields of vision, which differences may be processed to generate a thermal image.
Alternatively, both the object and the detector can remain stationary and the radiation may be modulated with a chopper that creates temperature differentials by alternately blocking and transmitting the incident radiation image. The chopper modulates the incident radiation so that the incident radiation periodically changes.
Mechanical choppers have several disadvantages. For example, portable choppers are battery operated and consume large amounts of power. Replacement battery packs are bulky and heavy, and limit the use of IR imaging in the field. In addition, choppers are noisy and mechanically complex so that they are prone to breakdown.